Products are commonly packaged in boxes, containers or cartons which may, for example, be formed from a paperboard material. Examples of such boxes, containers or cartons include cereal boxes, milk cartons, butter and margarine boxes and beer and soft drink secondary packaging (e.g., cartons enclosing a plurality of beer or soft drink cans or bottles). For explanatory purposes, the simple term “carton” may be used throughout this description to refer to the general type of boxes, containers or cartons described above.
A carton generally begins as a carton blank which is generally formed from a sheet of paperboard, although other materials are sometimes used. A carton blank will typically include various score lines about which the blank is to be folded, according to the desired configuration of the carton to be formed from the blank. After a carton blank is formed, it is often converted into a “knocked-down” carton. To form the knocked-down carton, the carton blank is typically folded about some, but not all of its score lines in such a way that, although it is partially formed, it still maintains a substantially flat configuration. This flat configuration facilitates space-efficient storage and/or transport of the knocked-down cartons prior to being filled with product.
A knocked-down carton is generally fed into machinery (usually a product filling machine) that opens the knocked-down carton from its flat configuration into what is commonly referred to an “erected carton”. In general terms, the filling machine then fills the erected carton with product and then completely seals the carton into a finished package ready for shipment and consumption.
Carton filling operations are typically carried out on high-speed automated machinery. As noted above, one of the first operations performed by this machinery is to open the knocked-down carton into an erected carton to facilitate introduction of product. This opening, in turn, involves the application of an “opening force” to the knocked-down carton for a given period of time. The period of time available depends upon the filling machine configuration and the speed at which the machine is being operated. The opening force applied by the filling machine causes the knocked-down carton to fold about various pre-scored fold lines. In the case of a carton having a rectangular cross-section, for example, erecting the knocked-down carton would require simultaneous folding about four parallel fold lines.
All knocked-down cartons exhibit some resistance to opening. This resistance is primarily associated with the energy required to fold the carton about the fold lines discussed above. If the opening resistance of a carton is too high, the knocked-down carton may fail to open properly when the opening force is applied by the filling machinery. This in turn, can cause the filling machine to jam and, thus, interfere with proper operation.
Some carton blanks are formed having a first (typically) paperboard layer and a second much thinner layer adhered thereto. The inner layer may, for example, be a paper material treated to be substantially impermeable to water and air (e.g., wax impregnated or laminated with plastic). In this manner, the inner layer can function as a liner and provide upper and lower flap portions such that it simulates a “bag-in-box” configuration. The outer layer is typically provided with scored fold lines to facilitate eventual transfiguration of the carton blank into a carton as generally discussed above. This type of carton blank is then typically converted into a knocked-down carton and, eventually, erected and filled, e.g., in a filling machine, in a manner as described above.